1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a carbon nano-tube tip. More particularly, the present invention provides an apparatus comprising a metallic vessel used as an electrode. The present invention provides a method comprising dropping a carbon nano-tube solution into the groove.
2. Background Art
A carbon nano-tube has a diameter of less than 1 μm which is smaller than that of a carbon fiber. Although there is no sharp line between carbon nano-tubes and carbon fibers, one narrow definition is that materials in which one face of carbon having a hexagon mesh is nearly parallel to the axis are referred to as carbon nano-tubes. Carbon nano-tubes include variant nano-tubes in which amorphous carbon is present around the carbon nano-tubes.
Generally, under the narrow definition, carbon nano-tubes are classified into two groups; (1) single-walled nanotubes (“SWNT”) which have one structure with a single hexagon mesh tube (grapheme sheet) and (2) multi-walled nanotubes (“MWNT”) which are comprised of multiple layers of graphene sheets. Since carbon nano-tubes have a diameter smaller than that of carbon fibers, a high Young's modulus, low work function, high heat conductivity, high chemical stability and high electrical conductivity, they have received much attention as a new industrial material.
Carbon nano-tubes are new materials made of only carbon atoms as a constituent and have Young's modulus of 1 Tpa or higher. Furthermore, since carbon nano-tubes are ballistic conductors, they can conduct a very large current, 109 A/cm2. Also, as carbon nano-tubes have a high aspect ratio, they can be used as a field electron emission source and they have been applied for the development of display or light emitting devices with high brightness. In addition, as some single-walled carbon nano-tubes show semiconductor properties, application to field effect transistor (FET) have been studied.
Carbon nano-tubes are thin and long enough to allow high accessibility to the target during manipulations. They can approach easily to the target without touching the adjacent object in a narrow space due to high aspect ratio. In addition, with high flexibility the carbon nano-tubes can prevent the target material from being damaged when tips are accidentally crashed on the target materials. With very high electrical conductivity, the carbon nano-tubes can be used as an electrode when researching electrical properties of the target material. Also, the high chemical stability of graphene sheets is one of the important properties that probe materials are supposed to have.
Conventionally, as a method for manufacturing carbon nano-tubes, electric arc discharge method was used. Recently, however, various methods have been attempted such as laser vapor deposition, pyrolysis vapor deposition, thermochemical vapor deposition, and plasma-enhanced chemical vapor deposition. As the carbon source in the said chemical vapor deposition, hydrocarbon gas such as acetylene, ethylene, methane, benzene and the like have been used and as catalytic metals, transition metals such as Ni, Co, Fe and so on or alloy thereof have been used.
Especially, if a solution containing catalytic metals is used for growing carbon nano-tubes, the catalytic metals are deposited on the substrate using ink-jet method, spray method, dipping method and the like and then dried the solution.
As a carbon nano-tube growth, the method of growing nano-tubes in vertical direction to the substrate, the method of growing carbon nano-tubes in the selected area by patterning catalytic metal on the substrate, and the method of growing carbon nano-tubes in the horizontal direction to use as an electronic device of nano size and the like have been suggested.
In electric arc discharge, a graphite rod as an anode and a cathode is engaged in arc discharge in an inert gas such as He, Ar and the like. As an anode includes Ni compounds, Fe compounds and rare-earth compounds, they can act as catalysts and synthesize single-walled carbon nano-tubes efficiently. However, as together with carbon nano-tubes, large amounts of amorphous carbon particles or graphite particles are simultaneously formed, they are all present in a form of mixture.
Laser vapor deposition synthesizes carbon nano-tubes by evaporating a specimen, which is made by mixing transition metals and graphite powder in a certain ratio inside the quartz tube with laser outside. Though such laser vapor deposition can synthesize carbon nano-tubes with considerably high purity, it has too low a productivity (Y. H. Lee et al., Carbon Science, “Synthesis and Applications of Carbon Nanotubes,” Vol. 2, No. 2 (2001) p. 123).
Chemical vapor deposition method grows carbon nano-tubes by decomposing acetylene and methane gas and the like containing carbon. Since chemical vapor deposition depends on the chemical reaction occurring in the pyrolysis process of methane gas and the like as a source, carbon nano-tubes with high purity can be produced. However, the structure of the manufactured carbon nano-tubes was is defective and imperfect than those of the carbon nano-tubes by arc discharge and the like.
In the pyrolysis method, liquid or gas phase hydrocarbon is supplied to the reaction tube in which transition metals are heated and decompose hydrocarbon. Then, carbon nano-tubes are continuously synthesized (Y. H. Lee et al., p. 127). The size of the transition metal is reported to be the main factor determining the diameter of the carbon nano-tubes. The size of such transition metal crystal is determined by the diffusion rate of the decomposed transition metal atoms and the concentration of decomposed transition metal per unit volume concentrated in the reaction space. It is not easy to control such diffusion rate and concentration, however.
Development of a nano probe that has the diameter of nano meter size is essential to move or manipulate objects in nano meter dimensions. Accordingly, the development of a nano probe using a carbon nano-tube has been carried out. As a part of the development of such a nano probe, the first requirement is to properly align carbon nano-tubes on a supporting body.
To date, direct growth method which mounts a carbon nano-tube directly on the supporting stand with chemical vapor deposition; the method in which CNT/polymer composite was thermally heated and physically cracked and then the carbon nano-tubes projecting from the end side are used as a tip; the method in which each carbon nano-tube are attached using adhesives in SEM; and the method in which an electric beam is irradiated between the tip and the carbon nano-tube having amorphous carbon in SEM/TEM to fix them have been reported.
Of those methods, although direct growth method has superiority in adhesion between supporting stand and the carbon nano-tubes, it is difficult to control the direction of the carbon nano-tubes. Furthermore, since the method using CNT/polymer composite can end up with multiple tubes, using it as a probe may be inadequate in manipulating the target materials. The case using a manipulator in SEM/TEM has inferior adhesion strength and directionality because the nano-tubes are attached using adhesive and an electron beam. With the conventionally available electrophoresis, it is difficult to control the bundle size and the direction of the carbon nano-tubes in SEM/TEM. (Jie Tang et al., Advanced Material, “Assembly of 1D Nanostructure into Sub-Micrometer Diameter Fibrils with Controlled and Variable Length by Dielecrophoresis,” Vol. 15(15) (2003))
FIG. 1 illustrates the use of a circular electrode for manufacturing carbon nano-tubes with electrophoresis. Since in the electrophoresis of the existing technique, the electric field is not aligned in one direction, but is diverged so that the distribution of the electric field is not focused, the angle between the tip and the surface of the organic solvent cannot be controlled so that the direction of the carbon nano-tubes at the end of the tungsten tip and the bundle of carbon nano-tubes cannot be controlled. FIG. 2 is a photograph showing the tip of the carbon nano-tubes manufactured according to electrophoresis of the existing technique of FIG. 1. As shown in FIG. 2, it can be recognized that the direction of the carbon nano-tubes at the end of the tungsten tip and the bundle of carbon nano-tubes is loosely formed.
Conventional methods for manufacturing a tip using carbon nano-tubes have problems in the direction of the carbon nano-tubes at the tip end, the diameter of each carbon nano-tube or bundle of carbon nano-tubes, the length of the attached carbon nano-tubes, adhesion strength of carbon nano-tubes and tip and the like.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.